Brushing tools for oil wells are well known in the art. Generally, these devices comprise a mandrel having radially extending brushes which may take the form of stiff bundles of wire which engage the interior walls of the oil well casing and/or perforations to be brushed or cleaned. A major problem associated with such devices is to assure that the radially extending brush elements are properly secured to the mandrel. In the event hard encrustations are encountered in the well casing, the brushes can become bent or broken off, or in some other manner disconnected from the mandrel itself and become lost in the bore hole.
Some proposed solutions to the above problem include providing a solid mandrel with diametric holes passing therethrough, the bundles of stiff wires in turn simply diametrically passing through the solid mandrel and extending radially from each end. This type of construction provides a very secure support for the wire brushes. On the other hand, the brushes are very difficult to replace if they become worn. A more serious problem is the fact that the solid mandrel will not permit circulation of fluid to be maintained during a brushing operation. While the circulation problem can be alleviated by providing a central bore in the mandrel for permitting circulation, the wire elements of the brushes diametrically criss-crossing the central bore impede the flow of such circulation.
Still other problems are encountered in that any openings or holes made to receive the bundle of wires forming the brushes tend to become worn as the tool is used. The wires themselves are of hard material and will tend to elongate radial holes from which the wires extend after repeated up and down brushing operations on the well casing surfaces.
In my U.S. Pat. No. 3,827,492 issued Aug. 6, 1974, I have provided an improved oil well brush tool which overcomes several of the foregoing problems. Essentially, the brush of this patent includes a mandrel with a central bore so that circulation can be maintained and a plurality of individual rings which surround the mandrel and support bundles of wires. While my tool shown in this patent will function to clean wells, the problem of the bundle of wires bearing against the openings in the individual rings as the brushes scrape along the side walls of the well result in elongation of the openings or a wearing away thereof. Further, the rings themselves must be sufficiently thick to provide adequate support for the bundles of wires and this thickness necessarily results in a reduction of the outside and inside diameters of the mandrels which the rings surround. As a consequence, effective circulation is somewhat impaired, although greatly improved over the heretofore noted other prior art devices. In addition, in the case of a plurality of rings as described in my above-referred to patent, there is involved a fairly lengthy amount of time to assemble and disassemble the brush tool.